Riddle Me This.........

[Captain Stubing]

Originally Posted by XA Coupsta

No man. The thrust is supplied by the engines.

Apologies... thrust from the engines, Lift from the shape and surface area of the wings.

{That's what I meant to think, anyway!}

[42.57lb]

Originally Posted by Casper

If this was the case than the X Plane jets dropped mid air by the US Airforce and then fired up in freefall wouldnt accellerate as there is no wall behind them at 30,000feet. Same as a 747 would be able to move off a normal runway as there is no wall behind them either.

sure a 747 can move off a run way without a way, but that's because the thrust provided by the engines produces a much higher force that the rolling resistance of the tyres on the ground, which is not moving in the other direction.

The reason for the wall or the ground for the rock is the same as when you squash a soft drink bottle and the top pops off, there is more air being forced into the space than there would nomally be, the only thing that can move is the rock (or the bottle top) because the friction of the air on the rocket is less than the force applied by the air behind the rocket being pushed out this is Action/Reaction,

BUT in the PLANE example there is a reaction and that is the run way conveyor moving in the opposite direction!

Can you even see where I'm coming from????

[XA Coupsta]

Originally Posted by 42.57lb

I think everyone has a fundamental mis-understading

You are a confident person. Everyone ELSE cept you has a misunderstanding!!!! lol
Tell that to the aerospace engineer or whatever his qualification was who also said this plane is gonna fly.

You arent comparing apples to apples in your rolling resistance argument. Same with the car thing - throw it out the window coz it doesnt apply!

Thrust/force - whatever you want to call it - in this example WONT be affected by any rolling resistance/whatever you want to call it. The comparison isnt valid as they dont relate to each other (again.......in this example)

[Casper]

Originally Posted by 42.57lb

I think everyone has a fundamental mis-understading

THRUST provides force - once one force is greater than another accleration occurs, once the forces are equal no acceleration occurs, so if you are travelling at a constant 100kph in your car it's because there is no net thrust or power. The rolling resistance of your tyres is equal to the thrust produced by your engine so you maintain your speed. The reason you slow down when you take your foot off the accelerator is because your rolling resistance is HIGHER than you driving thrust so you take your foot off the accelerator and you slow down right.

SAME applies while the plane is on the ground

This is correct. Now, what has more force. The rolling resistance of 2 small wheels.. or a bloody great big jet engine? Yes there is some rolling resistance but I think the jet engine would have more than enough thrust to overcome it.

[Mark351]

If the plane is travelling at 200kph on the conveyor belt, having accelerated at a rate twice that the conveyor belt can match...






















...how fast with Casper's XR6 travel down the 1/4 with his new high stall torque converter??

:monkes:

[Captain Stubing]

Originally Posted by Casper

This is correct. Now, what has more force. The rolling resistance of 2 small wheels.. or a bloody great big jet engine? Yes there is some rolling resistance but I think the jet engine would have more than enough thrust to overcome it.

Can't we talk about a Cessna???

[flappist]

Originally Posted by 42.57lb

I think everyone has a fundamental mis-understading

THRUST provides force - once one force is greater than another accleration occurs, once the forces are equal no acceleration occurs, so if you are travelling at a constant 100kph in your car it's because there is no net thrust or power. The rolling resistance of your tyres is equal to the thrust produced by your engine so you maintain your speed. The reason you slow down when you take your foot off the accelerator is because your rolling resistance is HIGHER than you driving thrust so you take your foot off the accelerator and you slow down right.

SAME applies while the plane is on the ground

Not everyone, just you and a few others,

The conveyor is NOT push against the thrust, it is pushing against the outside surface of a wheel and ALL of the force is converted to rotational force on the wheel making it spin. NONE of it is transferred to the axel of the wheel and therefore the plane.

Go and get a pushbike, turn it upsidedow and the move it by only pushing on the top of the wheel.....

Get it now?

[DOC]

Originally Posted by tx3dude

you said yourself a plane moving forward(relative to the ground) is doing 10kph...

No i asked a question, how fast would the wheels be going if it was being thrusted at 10KPH, the answer was 10KPH, so now we put those wheels on the treadmill running at 10KPH in the reverse direction,

yes the plane is travelling at 10KPH agreed but with the tarmac travelling in the opposite direction at 10kph even though the plane is travelling at 10kph it would appear to remain static ( you could stand along side it and it would not move ) with this in mind it then seems hard for me to see how any air is passing over the wings thus no lift and no take off.

back in my corner. :

[42.57lb]

Originally Posted by Casper

This is correct. Now, what has more force. The rolling resistance of 2 small wheels.. or a bloody great big jet engine? Yes there is some rolling resistance but I think the jet engine would have more than enough thrust to overcome it.

Awesome we agree!!! Now, all I'm saying is, that the problem states that the tarmac moves at the same rate such that: if the plane had a ground speed of 200kph, Then the coveyor would move at 200kph?

The plane is moving thus ----> at 200kph

the tarmac is moving thus <----- at 200kph

the whole point is that 200 + -200 = 0?

[Charliewool]

Originally Posted by Dave_au

This thread still going!

Answer from an aerospace engineer:

hala lulah!...

:

[Casper]

Originally Posted by 42.57lb

sure a 747 can move off a run way without a way, but that's because the thrust provided by the engines produces a much higher force that the rolling resistance of the tyres on the ground, which is not moving in the other direction.

The reason for the wall or the ground for the rock is the same as when you squash a soft drink bottle and the top pops off, there is more air being forced into the space than there would nomally be, the only thing that can move is the rock (or the bottle top) because the friction of the air on the rocket is less than the force applied by the air behind the rocket being pushed out this is Action/Reaction,

BUT in the PLANE example there is a reaction and that is the run way conveyor moving in the opposite direction!

Can you even see where I'm coming from????

So your whole position is that a plane can take off from a standard runway because the thrust is greater than the rolling resistance of the wheels.. but if you make the wheels turn faster than the plane is actually going than the rolling resistance suddenly becomes so huge that the thrust cant compensate? Seriously.. you can put some planes on square wheels made of concrete and the rolling resistance still wouldnt be enough to stop the engines thrust from pushing it forward quick enough to take off.

[42.57lb]

Originally Posted by flappist

Not everyone, just you and a few others,

The conveyor is NOT push against the thrust, it is pushing against the outside surface of a wheel and ALL of the force is converted to rotational force on the wheel making it spin. NONE of it is transferred to the axel of the wheel and therefore the plane.

Go and get a pushbike, turn it upsidedow and the move it by only pushing on the top of the wheel.....

Get it now?

Sorry dude, there is no perfect energy tranfer, a large protion of the energy is traferred into heat, and that heat is caused becasue of the resistance. why do you get carpet burn?

[Mark351]

If a Cessna travelling down a conveyor belt falls in the forest...













...should Casper get a body kit for his XR6?

:

[Dave_au]

This qu fooled me too - the question doesnt actually say the aircraft is kept stationary. In this hypothetical, the plane does actually travel down the conveyor belt as if it were an actual runway - and runs a length probably a little longer than it's conventional runway length.

Think of tieing a cable from a winch (not on conveyor) to a model car on a conveyor belt. Match the speed of the conveyor belt to the winch - say 20cm/s. The winch will pull the car in at this speed, the conveyor will go against it. The wheels on the model car would be rotating at 40cm/s.

[Ghiadude]

The plane is moving thus ----> at 200kph relative
to ground and air that its engiones are pusing against
the tarmac is moving thus <----- at 200kph relative to the graound and the air that the engines are pushing against

the whole point is that 200 + -200 = 0 yes but the equation is flawed...the plane is moving 400kmh relative to treadmill belt, and 200kmh(takeoff speed relative to ground)

[42.57lb]

Originally Posted by Casper

So your whole position is that a plane can take off from a standard runway because the thrust is greater than the rolling resistance of the wheels.. but if you make the wheels turn faster than the plane is actually going than the rolling resistance suddenly becomes so huge that the thrust cant compensate? Seriously.. you can put some planes on square wheels made of concrete and the rolling resistance still wouldnt be enough to stop the engines thrust from pushing it forward quick enough to take off.

yeah, but the runway would stiff have to stationary. The point is that for the purpose of this hypothetical, the coveyor moves... Whether they were round or not, if you had thrust and a conveyor equaling that thrust, the plane would still remain stationary

[Casper]

Originally Posted by 42.57lb

Awesome we agree!!! Now, all I'm saying is, that the problem states that the tarmac moves at the same rate such that: if the plane had a ground speed of 200kph, Then the coveyor would move at 200kph?

The plane is moving thus ----> at 200kph

the tarmac is moving thus <----- at 200kph

the whole point is that 200 + -200 = 0?

no, it woudl be 200 + 200 = 400. That how fast the wheels would be turning. The plane would still be doing 200kph.. and take off. The convayor cant stop this, all it can do is make the wheels turn faster. The wheels are freespinning, the convayors actual force on the axles (and therefore the actual body of the plane) is 0.

[Captain Stubing]

Originally Posted by Dave_au

This qu fooled me too - the question doesnt actually say the aircraft is kept stationary. In this hypothetical, the plane does actually travel down the conveyor belt as if it were an actual runway - and runs a length probably a little longer than it's conventional runway length.

Geez, Dave! you put it like that... Plane doing the normal takeoff, wheels going twice as fast.... MYTHBUSTERS???!!!

[42.57lb]

Originally Posted by tx3dude

The plane is moving thus ----> at 200kph relative
to ground
the tarmac is moving thus <----- at 200kph relative to PLANE ONLY

the whole point is that 200 + -200 = 0 yes but the equation is flawed...the plane is moving 400kmh relative to treadmill belt, and 200kmh(takeoff speed relative to ground)

So what you're saying is that the coveyer is not moving realtive to ANYTHING except the plane. How is that possible? There are only 4 dimenions?!?!?!?!

point a on the conveyer moves at 200kph relative to teh earth, however the nature of teh conveyer is that i'ts belt can move the fixture remains stationary.

I if wer on a conveyer, you were on the gound and the conveyer was moving and you were not would I not be moving relative to you (and you are on the ground)?

[XA Coupsta]

But the conveyor is not equalling that planes thrust at all!!!!!

[Ghiadude]

Originally Posted by 42.57lb

So what you're saying is that the coveyer is not moving realtive to ANYTHING except the plane. How is that possible? There are only 4 dimenions?!?!?!?!

point a on the conveyer moves at 200kph relative to teh earth, however the nature of teh conveyer is that i'ts belt can move the fixture remains stationary.

I if wer on a conveyer, you were on the gound and the conveyer was moving and you were not would I not be moving relative to you (and you are on the ground)?

plse re read my post as i made a few mistakes now edited..

[Casper]

Originally Posted by 42.57lb

yeah, but the runway would stiff have to stationary. The point is that for the purpose of this hypothetical, the coveyor moves... Whether they were round or not, if you had thrust and a conveyor equaling that thrust, the plane would still remain stationary

how can a conveyor counteract thrust? It cant. The plane does not drive forward from the wheels. The wheels are not the force driving forward. What you are saying is that even though thrust is totally based on the force of air the conveyor can still stop it because the wheels are touching it. Thats like saying that the conveyor could stop a hovercraft moving forwards because he fingers of its skirt are touching it.

[42.57lb]

Originally Posted by Casper

no, it woudl be 200 + 200 = 400. That how fast the wheels would be turning. The plane would still be doing 200kph.. and take off. The convayor cant stop this, all it can do is make the wheels turn faster. The wheels are freespinning, the convayors actual force on the axles (and therefore the actual body of the plane) is 0.

DUDE!!!!

if the palne was moving ----> @ 200
and
the tarmac was moving @ 200 ---->

it would be 200 + 200, BUT they're not moving the same way. This is fundamental to the hypothetical. Srely the direction that the wheels spin is irrelevant

[Captain Stubing]

Casper, I apologise. You may be right!

[Charliewool]

Originally Posted by charliewool

Looks like we're not the only nutters pondering this!... A google search "Will the plane take off" produced a heap of other forums arguing on this.. the one below has FORTY SIX pages & they're still going round in circles! lol

http://community.discovery.com/group...6/m/7451937218

Reckon we can get to 47 or what?

(Casper, you need a knighthood)

[42.57lb]

Originally Posted by Casper

Thats like saying that the conveyor could stop a hovercraft moving forwards because he fingers of its skirt are touching it.

Would you not agree that if the friction was great enough it could?

[Ghiadude]

Originally Posted by swanny

Casper, I apologise. You may be right!

welcome and thank god!! and casper!

[Ghiadude]

Originally Posted by 42.57lb

Would you not agree that if the friction was great enough it could?

it would have to equal the thrust created by the forward propelling engines... if this was the case airplanes would not leave the ground... the friction of the wheel bearings would stop them... do you see?

[Casper]

Originally Posted by 42.57lb

Would you not agree that if the friction was great enough it could?

I would.. but how would it create that much friction. The same would apply to a normal runway though. If the engine wasnt that powerful and you had square wheels it wouldnt take off on any surface. The conveyor alone on a normal plane simply wouldnt create any more significant friction then on a normal runway. Therefore the plane will take off.

[flappist]

Originally Posted by 42.57lb

Awesome we agree!!! Now, all I'm saying is, that the problem states that the tarmac moves at the same rate such that: if the plane had a ground speed of 200kph, Then the coveyor would move at 200kph?

The plane is moving thus ----> at 200kph

the tarmac is moving thus <----- at 200kph

the whole point is that 200 + -200 = 0?

No 200km/h minus (not plus they are in opposite directions) -200km/h = 400km/h, the speed of the wheels.

The axels of the conveyor rollers are going 0km/h,
The air is going 0 km/h
The conveyor belt is going 200 km/h -->
The plane 200km/h <--
Wheels 400km/h

V1, rotate, gear up, trim for best climb, "Traffic Loony CTAF, Alpha Foxtrot Foxtrot, bugsmasher has departed 43, on climb to any altitude and turning onto any heading away from here, traffic Loony CTAF"